In the past, a color filter (written as CF in the following) to pass the light of red, green, and blue (written as RGB in the following) is inserted in a light path to a pixel, and photoelectric conversion is performed with a photodiode (written as PD in the following) formed in the pixel. Consequently, a color image is produced with the constitution in which a red, green, and blue (RGB) electrical signal are independently obtained for every pixel respectively.
Since the system which performs a color separation by the RGB-CF requires a pixel dedicated for every color, three RGB pixels are necessary in order to obtain a color electrical signal in a set of at least three pixels, such as RGB.
Since it is necessary to make light transmit an RGB-CF, light energy is converted into heat by the RGB-CF and decreases, and the transmitted light energy which has decreased is irradiated to PD. Therefore, there arises a problem that the photoelectron after photoelectric conversion decreases and an output chrominance signal is reduced, as well as a problem that the heat generation by the RGB-CF varies the spectroscopic property of the RGB-CF. Another problem is decrease of light use efficiency, due to the thickness of the RGB-CF layer which narrows the angle of available incident light. Since a pigment is used for the material of an RGB-CF, in order to protect a wafer manufacturing process line from contamination by the heavy metal included in the pigment, an exclusive RGB-CF manufacturing line, separated from the wafer manufacturing process line, needs to be provided.
As a means to solve these problems, Patent Document 1 and Patent Document 2 propose a system in which a color electrical signal, such as RGB, is obtained without using an optical color filter, such as an RGB-CF. Patent Document 1 proposes a color image sensing device in which PN junctions of plural numbers of depth are constituted, by laminating several layers of semiconductor region with alternately different conductive types; accordingly, photoelectric conversion is performed for light in different plural wavelength band regions by the PN junctions of plural numbers of depth, respectively.
Patent Document 2 proposes a color image sensing device in which, in order to obtain RGB chrominance signals by a single pixel without using an RGB-CF, PN junctions of plural numbers of depth are constituted, by laminating several layers of semiconductor region with alternately different conductive types; accordingly photoelectric conversion is performed for light in different plural wavelength band regions by the PN junctions of plural numbers of depth, respectively.
Patent Document 1 and Patent Document 2 both propose elements in which PN junctions of plural numbers of depth are constituted, by laminating several layers of semiconductor region with alternately different conductive types, accordingly photoelectric conversion is performed for light in different plural wavelength band regions by the PN junctions of plural numbers of depth, respectively. According to the elements, a semiconductor is irradiated without using an RGB-CF and there is no attenuation of the light in the RGB-CF when compared with an RGB-CF system, therefore, as one of features, the effective utilization efficiency of light is high. It is not necessary to constitute three pixels independently in two dimensions for every RGB, and three chrominance signals of RGB can be obtained independently from one pixel. Therefore, it is possible to reduce the PD occupied area of a pixel to one third, compared with an RGB-CF system, and it is also possible to attain about three times better resolution than the RGB-CF system, and about three times higher sensitivity than the RGB-CF system.
[Patent Document 1] Japanese Unexamined patent Publication No. Sho 61 (1986)-187282.
[Patent Document 2] Japanese Unexamined patent Publication No. 2003-298038.